The present invention relates to a passenger detection apparatus for detecting the existence of a passenger in an automobile for use in an airbag system, an antitheft system, etc.
An airbag expands between a passenger and a framework, such as a dashboard, etc., at the time of an automobile collision to protect the passenger. However, the airbag is expensive and the expansion thereof with no passenger involves a heavy economic burden. Hence, a control has been exercised by which an airbag is expanded depending on the existence of a passenger at the time of collision. Also, in case there is an intruder in an automobile, it is necessary to detect this occupancy and take a coping measure.
As a passenger detection apparatus for this purpose, for example, the one described in the Unexamined Japanese Patent Application Publication No. Hei 05-139233 is known. The construction of this apparatus will be explained with reference to FIG. 7. In the figure, the reference numeral 540 depicts a rubber pad spread on an automobile seat, 550 a plurality of piezoelectric film sensors fixed to the pad 540, and 560 a plurality of weight sensors fixed to the pad 540.
Next, the operation will be explained. When a passenger sits on the seat, the piezoelectric film sensors in the portion on the passenger are flexed, then producing electrical pulses. Also, the weight sensors are flexed to cause a change in the resistance thereof. Thus, monitoring the output of the sensors 550 and 560 enables determination of the existence of a passenger and the boarding position of the passenger.
Since the conventional passenger sensor is arranged as above, a passenger cannot be detected unless the passenger is in the position in contact with the sensor. Therefore, there is a problem that, in order to detect the existence of a passenger even in case the passenger boards in a position out of a normal boarding position, a multiplicity of sensors are required to be provided in a wide range, thus resulting in a high cost.
Also, as a method for detecting a wide-ranging pressure by one sensor, as disclosed in the Unexamined Japanese Patent Application Publication No. Hei 10-029495 and No. 2000-062565, etc., there is suggested a method in which a bladder having fluid sealed therein is provided inside a seat and a pressure sensor detects a pressure increase inside the bladder caused by the passenger weight. However, this method has a problem that, since the sensor cannot attain its function when the preload inside the bladder is deflated, a sealing structure for maintaining the preload is required and it is difficult to make this structure durable, still allowing no moderate-price production.
The invention has been-made to solve the aforesaid problems and an object thereof is to obtain a passenger detection apparatus which can cover a wide range in a simple construction.
The passenger detection apparatus according to the invention includes force transmission thread which is subjected to a tensile force by a power point arranged on a place, such as a seat, a floor surface, a wall surface or the like, which may possibly be displaced through contact with a passenger, a means for tensioning the force transmission thread, and a means for detecting the displacement of the force transmission thread.